1. Field of the Invention
This application generally relates to data storage facilities used in data processing networks and more specifically to the analysis of operations of multiple redundant data storage facilities interconnected by a communications path.
2. Description of Related Art
The above-referenced U.S. Pat. No. 6,209,002 discloses a data storage facility for transferring data from a data altering apparatus, such as a production data processing site to a remote data receiving site. The data storage facility includes a first data store for recording each change in the data generated by the data altering apparatus. A register set records each change on a track-by-track basis. A second data store has first and second operating modes. During a first operating mode the second data store becomes a mirror of the first data store. During a second operating mode the second data store ceases to act as a mirror and becomes a source for a transfer of data to the remote data receiving site. Only information that has been altered, i.e., specific tracks that have been altered, are transferred during successive operations in the second operating mode. Commands from the local production site initiate the transfers between the first and second operating modes.
One of the advantages of the foregoing system relates to the required characteristics or a communications path between the remote site and the data receiving site. That is, it is expected that the required bandwidth of that communications path will be significantly less than the required bandwidth of the communications path between the local production site and an intermediate remote storage location. As will be apparent, if the bandwidth of this communications path decreases, the costs for the communications path will also decrease. However, the ultimate decrease will be dependent upon the time that can be allocated to the receipt of all changes at the remote data receiving site. Consequently it is desirable to provide some method of estimating, with some accuracy, the bandwidth requirements required for enabling all updates to transfer to the data receiving site within acceptable times. Conversely, it is desirable to provide some method of estimating the time required to transfer all updates to the data receiving site given an available bandwidth of the communications path. If such information is available, then it is possible to tailor the communications path to provide the desired performance at the least cost.
Stated differently, assume that a customer wishes to add the cascading feature described in the above-identified U.S. Pat. No. 6,209,002. It would be helpful to predict the communications path requirement in advance of installing the cascading feature to avoid overly long updating because the bandwidth is too low or to avoid extra charges because the bandwidth is too high.
It might seem that one of several utilities available in data processing networks might provide the information from which the performance/bandwidth could be predicted. For example, the MVS operating system includes a utility that records each I/O operation. However, that information does not distinguish read and write operations and does not provide any information with respect to logical volumes involved in any I/O requests. Symmetrix data storage facilities provided by the assignee of this invention can monitor read and write requests at a logical volume level, but they also do not provide sufficient information. Consequently, what is needed is a method and apparatus for enabling a system engineer or customer to predict, with reasonable accuracy, the rate at which data will transfer between a remote site and a data receiving site.